Being obese in childhood may be associated with increased cardiovascular morbidity and mortality in adulthood. We examined the relationship between obesity and overweight identified in youth and carotid artery intima-media thickness assessed in adulthood. As part of the longitudinal Cardiovascular Risk in Young Finns Study, we assessed tracking of body mass index (BMI) from youth (ages 3-18 years) to young adulthood (ages 24-39 years) in a cohort of 2,260 subjects. BMI measured in youth was significantly associated with BMI measured in adulthood. The risk of being obese in adulthood (BMI > 30 kg/m(2)) was increased by three-fold in subjects who had been overweight or obese (BMI > 80th percentile) in childhood (ages 3-9 years) and by four-fold in subjects who had been overweight or obese in adolescence (ages 12-18 years). Age and sex adjusted adult IMT values were comparable in subjects who had been consistently overweight/obese in youth and adulthood and in subjects who became obese in adulthood, 0.642 mm versus 0.634 mm, respectively. IMT values were lower (overall P < 0.0001) and comparable in subjects who had remained consistently non-obese and those who had been obese in youth but had become non-obese in adulthood, 0.610 mm versus 0.627 mm, respectively. We conclude that being obese in youth is associated with increased carotid IMT in adulthood, but this relationship is explained by significant tracking of body mass from youth to adulthood.